CAIRO — Representatives from across Egypt’s political spectrum held a rare meeting Thursday to denounce violence, hours before a fresh call for a new wave of mass protests across the country aimed at pressuring President Mohammed Morsi, an Islamist, to accept opposition demands to form a national government and amend the constitution.

Hosted by Egypt’s premier Islamic institution, Al-Azhar, the country’s two rival factions of Islamists and secular-leaning opposition grouping The National Salvation Front pledged to work to halt violence. The meeting followed a week of political rioting that exploded across the nation and left as many as 60 people dead.

Egypt’s Muslim Brotherhood and the ultraconservative Salafis along with their rival liberal parties vowed to condemn the instigation of violence, prohibit it, and differentiate between a ‘‘political act and sabotage.’’

‘‘Denouncing violence in all its forms and shapes, condemning it clearly and decisively, criminalizing it nationally, and prohibiting it religiously,’’ a statement signed by all the attendees said. ‘‘Abiding by peaceful political means . . . abiding by the serious dialogue,’’ it said.

It was the first meeting between the Muslim Brotherhood and the opposition National Salvation Front since the front was formed in November.

The meeting sparked angry reaction from activists and youth groups who accused the liberal opposition of making political compromises despite bloodshed. Security forces continued to clash with rock-throwing protesters in downtown Cairo for an eighth day. And Egyptian authorities continued a wave of arrests and kidnappings of protesters, including members of the Black Bloc who wear black masks and vow to ‘‘defend the revolution’’ from Islamists. Hundreds of protesters were arrested during the past week.

In one latest incident, the liberal Popular Current party accused security forces of abducting and torturing one of its members, Mohammed el-Gendi, who disappeared for four days before showing up in a Cairo hospital in a serious condition.

‘‘This is premeditated and signals a return of old practices of abductions, torture, and assault,’’ the party said in a statement.

Security forces were not available for comment.

Hussein Abdel-Ghani, a member of the front, denied that the opposition was making compromises but said, ‘‘the youth defeated the Mubarak state with their bare chests. . . . peaceful means are among the revolution principles.’’ However, he stressed that there would be no dialogue unless Morsi ordered security authorities not to use violence with protesters.

‘‘No dialogue before the bloodshed stops,’’ he said.

Police abuse and maltreatment were among the reasons for the country’s 2011 uprising.

The Islamists-liberals meeting also comes ahead of a fresh wave of mass protests expected across the country and at the presidential palace. In a new statement, the National Salvation Front called upon Egyptians to express ‘‘firm rejection to a regime that insists on imposing its singular will on the people and to administer the country to serve the interest of the Muslim Brotherhood group.’’

The front reiterated a list of demands including setting up a nationally unified government and rewriting controversial parts of the constitution in addition to investigating the latest deaths.

Morsi rejected calls for forming a new government, in remarks he delivered during a news conference with German Chancellor Angela Merkel during his short visit to Berlin.

Violence escalated after the opposition called for protests to mark the second anniversary of the Jan. 25, 2011, uprising, which ended rule of authoritarian president Hosni Mubarak.

Since then, violence has spread around the nation — the worst occurring in the Suez Canal city of Port Said, which has declared itself independent in the revolt against Morsi’s government. Nile Delta provinces also have witnessed street clashes and riots.